PROJECT SUMMARY/ABSTRACT The overarching goal of this proposal is to advance our knowledge of early brain development by mapping temporally precise developmental trajectories of brain network topology and dynamics during the first 6 months of life, a period of unparalleled postnatal growth and change. Describing the developmental trajectory of brain systems during this formative period has the potential to provide groundbreaking insights into major areas of scientific inquiry, including the identification of brain systems that underlie the development of cognitive functions, the discovery of how structural and functional network specializations arise, and the identification of brain networks that contribute to neurodevelopmental disability. Using a novel non-uniform longitudinal sampling design and advanced non-parametric curve fitting techniques, the proposed project will map four- dimensional, temporally accurate developmental trajectories of brain structural and functional networks in typically developing infants between birth and the 6th month of life (Aim 1). These connectomes will be made publicly available to the research community. In Aim 2, the latest advances in dynamic network science will be applied to identify community structure (i.e., modules of densely inter-connected brain regions) in time-varying infant brain networks. Finally, fine scale changes in the community dynamics of infant brain networks will be characterized to understand how modules and their interactions change over developmental time (Aim 3). Analyses will be conducted on anatomical, diffusion, and resting-state functional MRI data collected from infants at non-uniform, densely sampled time points between birth and 6 months. The success of the project will significantly advance our understanding of the dynamic processes of brain network development in early infancy, a pivotal, and yet relatively uncharted, period of development.